Method and control device for controlling a regeneration process of an exhaust gas particle filter

ABSTRACT

The invention relates to a method ( 61 ) for controlling a regeneration process of an exhaust gas particle filter ( 41 ) of an internal combustion engine ( 11 ), wherein said method ( 61 ) comprises safeguards ( 71 ) for protecting said exhaust gas particle filter ( 41 ) from overheating and when implementing said safeguards ( 71 ) a gas flow (m a ) of the gas flowing through the exhaust gas particle filter ( 41 ) is reduced ( 71   a,    71   b ) for the purpose of restricting a reaction rate of an exothermal reaction taking place in said exhaust gas particle filter ( 41 ) during the regeneration process. In order to allow for an efficient regeneration of an exhaust gas particle filter ( 41 ) and still avoid damage to or the destruction of said exhaust gas particle filter ( 41 ) as a result of the overheating thereof, the invention is characterized in that during the regeneration process an instantaneous value (x(t)), which characterizes an instantaneous mass (x) of the soot situated in the exhaust gas particle filter ( 41 ), is ascertained, a check ( 67 ) is made as a function of the instantaneous value (x(t)) to determine whether said exhaust gas particle filter ( 41 ) is in an uncritical operating state and said safeguards ( 71 ) are suppressed in the event that the uncritical operating state is present.

This application is claims benefit of Serial No. 10 2009 026 630.5,filed 2 Jun. 2009 in Germany and which application is incorporatedherein by reference. To the extent appropriate, a claim of priority ismade to the above disclosed application.

TECHNICAL FIELD

The invention relates to a method for controlling a regeneration processof an exhaust gas particle filter of an internal combustion engine,wherein the method comprises safeguards for protecting the exhaust gasparticle filter from overheating and a gas flow of the gas flowingthrough the exhaust gas particle filter is reduced for limiting areaction rate of an exothermal reaction taking place during theregeneration process. In addition the invention relates to acorresponding control device of an internal combustion engine, which isdesigned for carrying out such a method.

BACKGROUND

Internal combustion engines for motor vehicles, particularly dieselinternal combustion engines, often have an exhaust gas particle filterfor filtering out contaminated particles, particularly soot particles,from the exhaust gas produced by the internal combustion engine. Suchexhaust particle filters are usually disposed in the exhaust gas tractof the internal combustion engine so that they have exhaust gas, whichis discharged from the combustion chambers of the internal combustionengine, passing through them during the operation of said internalcombustion engine. During the operation of the exhaust gas particlefilter, pollutants filtered out of the exhaust gas are embedded in theform of soot in said exhaust gas particle filter. A regeneration processtakes place from time to time during the operation of the exhaust gasparticle filter, wherein soot situated in said exhaust gas particlefilter is burned. In order to initiate the regeneration process, theinternal combustion engine is normally operated such that thetemperature of the exhaust gas flowing into the exhaust gas particlefilter is so substantially raised that the soot embedded in said exhaustgas particle filter begins to burn off. Normally an exhaust gastemperature of approximately 600EC to 650EC is adjusted to perform saidprocess. Because such high exhaust gas temperatures, particularly indiesel internal combustion engines, are at best achieved during normaloperation in the full load range, the internal combustion engine isusually intentionally operated at an inefficient operating point,whereat said internal combustion engine has a relatively high heatoutput in comparison to its mechanical output.

For this purpose, a fuel injection system of the internal combustionengine can accordingly be operated. A main injection of fuel into thecombustion chambers of the internal combustion engine can be temporallyretarded, or an afterinjection, which temporally follows the maininjection, can be provided. The afterinjection can be temporallydefined, such that fuel injected into the combustion chambers during theafterinjection, still combusts within the combustion chambers. Provisioncan, however, also be made for the fuel injected by means of theafterinjection to first combust in the exhaust gas system of theinternal combustion engine, particularly in an oxidation catalyticconverter of the exhaust gas system. Suitable adjustment interventionsin the air system of the internal combustion engine can be performed toraise the exhaust gas temperature. For example, a throttle valvedisposed in an intake manifold of the internal combustion engine can atleast partially be closed in order to reduce the gas flow through saidinternal combustion engine and therefore also the mass flow of the airflowing into said internal combustion engine so that a relatively smallamount of the air has to be heated to the high temperatures per unit oftime.

Because the combustion of the soot embedded in the exhaust gas particlefilter relates to an exothermal reaction, the danger exists for theexhaust gas particle filter to overheat during the regeneration processand thermally critical filter materials within the exhaust gas particlefilter to thereby be destroyed. The regeneration process must thereforebe controlled such that a reaction rate of the exothermal reaction islimited. Measures for limiting the oxygen supply to the exhaust gasparticle filter are thus provided. The oxygen supply can on the one handbe implemented by the corresponding control of the injections of fuelinto the combustion chambers of the internal combustion engine and onthe other hand by limiting a mass flow of the gas flowing into theexhaust gas particle filter.

A method for controlling a regeneration of an exhaust gas particlefilter is known from the German patent publication DE 10 2006 010 095A1, wherein adjustment interventions at the throttle valve and at adevice for recirculating the exhaust gas are performed in order toprotect the exhaust gas particle filter from damage to due tooverheating.

Whereas the publication mentioned above shows a measure for reducing thereaction rate, a method for controlling an internal combustion engine isknown from the European patent publication EP 1 364 110 B1, wherein adecision can be made whether measures for reducing the reaction ratehave to be taken. According to this method, a parameter is ascertained,which characterizes a future intensity of the exothermal reaction. Thestated measure is taken if this parameter exceeds a threshold value.Whether the measure for limiting the reaction rate is to be taken, isdecided according to the invention before the beginning of theregeneration process with the aid of a prognosis. Because such aprognosis is subject to relatively large uncertainties, the thresholdvalue must be chosen such that damage to or destruction of the exhaustgas particle filter as a result of it overheating can be eliminated inevery conceivable case. As a result, the exothermal reaction during mostof the regeneration processes takes place with a significantly smallerreaction rate than would be possible without overheating the exhaust gasparticle filter and the regeneration process thereby lasts a relativelylong time. This leads to a relatively high fuel consumption of theinternal combustion engine because its inefficient operating point mustbe maintained quite long for the regeneration of the exhaust gasparticle filter.

SUMMARY

It is the aim of the present invention to provide a method, respectivelya control unit, which allows for an efficient regeneration of an exhaustgas particle filter with little fuel consumption by the internalcombustion engine, and nevertheless avoids damage to or the destructionof the exhaust gas particle filter as a result of it overheating. It istherefore the aim of the invention to improve a so-called regenerationefficiency of the regeneration process.

When implementing the method according to the invention, theinstantaneous value for the current mass of soot situated in the exhaustgas particle filter is maintained and regularly updated at least duringthe regeneration process. This value is used to control the regenerationprocess. As a result, a reaction rate of the exothermal reaction can beascertained at each point in time during the regeneration process, andthe exothermal reaction can be controlled such that the temperaturewithin the exhaust gas particle filter relatively markedly approaches amaximum admissible temperature within the exhaust gas particle filterwithout the danger existing of damage to or the destruction of theexhaust gas particle filter as a result of an overheating of saidexhaust gas particle filter.

With the aid of the instantaneous value, a check can be made relativelyaccurately and reliably to determine whether the exhaust gas particlefilter is even in a critical operating state, wherein the danger existsthat it can be damaged or destroyed by the exothermal reaction. If thisis not the case—if the exhaust gas particle filter is thus in anuncritical operating state—the safeguards are then suppressed. Thatmeans that they are not implemented even if they appear necessary due toother indicators as for example a high prognosis value ascertainedbefore the beginning of the regeneration process. A quick regenerationof the exhaust gas particle filter hereby occurs at a on averagecomparatively high reaction rate. That means that a comparatively higherdegree of regeneration efficiency is achieved by means of the methodaccording to the invention.

It is particularly preferred for the uncritical operating state to berecognized in the event that the instantaneous value is smaller than apredetermined minimum value. It has in fact been shown that aninadmissibly high temperature of the exhaust gas particle filter can nolonger be achieved if only a relatively small quantity of soot isembedded in the exhaust gas particle filter. In such a case, thesafeguards can be eliminated without risk. In the case of small sootmasses, a relatively fast regeneration is achieved by suppressing thesafeguards. It is conceivable for the safeguards to be initiallyimplemented at the beginning of the regeneration process and for saidsafeguards to be suppressed during the regeneration process as soon asthe instantaneous value has dropped below the predetermined minimumvalue. That means the reaction rate is initially limited by decreasingthe gas flow; and subsequently as soon as the uncritical operating stateis achieved, the gas flow is no longer decreased so that the reactionrate is consequently no longer limited. In so doing, an efficientreaction is achieved toward the end of the regeneration process, wherebythe degree of regeneration efficiency is increased.

As an alternative to or in addition to this, provision can be made forthe uncritical operating state to be recognized in the event that a gastemperature of the gas flowing into the exhaust gas particle filter islower than a predetermined first minimum temperature. This is the casebecause an overheating of the exhaust gas particle filter can at leastsubstantially be ruled out if the gas temperature is relatively low evenwhen the reaction rate is high. The safeguards are not required in sucha case and also not desired because they would only unnecessarilyprolong the duration of the regeneration process.

In addition to the check during the regeneration process to determinewhether the critical or uncritical operating state is present, provisionis made in a preferred embodiment of the invention for a check to bemade already prior to the beginning of the regeneration process todetermine whether the safeguards are required. Provision canparticularly be made in this preferred embodiment for an initial valueto be ascertained, which characterizes the mass of the soot situated inthe exhaust gas particle filter prior to the beginning of theregeneration process. Secondly a check is made as a function of saidinitial value to determine whether the reaction rate during theregeneration process is anticipated to be too high. Finally saidsafeguards are only then carried out in the event that the checkrevealed that the reaction is anticipated to be too high.

The danger exists at a relatively low gas temperature that due to thegas flow the temperature of the exhaust gas particle filter is reducedto such an extent that the exothermal reaction at least largely comes toa standstill, i.e. the regeneration is discontinued before all of thesoot deposits have been burned off in the exhaust gas particle filter.In order to avoid such a premature termination of the regeneration,provision can be made for the gas flow to be reduced to avoid a coolingof the exhaust gas particle filter in the event that the gas temperatureis lower than a predetermined second minimum temperature. In so doing,it is ensured that each regeneration process is carried out reliably andcompletely. A high degree of average regeneration efficiency thusresults.

It is particularly preferred for the gas flow to be manipulated byadjusting the actuating elements of an air and exhaust gas system of theinternal combustion engine, preferably by adjusting a degree of openingof a throttle device and/or an exhaust gas recirculation valve. It isparticularly preferred with regard to reducing the gas flow for thethrottle device to be at least partially closed and the exhaust gasrecirculation valve to be at least partially opened. As a result ofthese actions, at least a part of the gas flowing through the combustionchambers of the internal combustion engine is recirculated beforereaching said combustion chambers via the exhaust gas recirculationvalve disposed in the exhaust gas return channel. In so doing, thequantity of exhaust gas flowing through the exhaust gas particle filteris reduced.

Provision is made in the present invention for the instantaneous value,preferably model based, to be ascertained as a function of at least onestate variable, which characterizes an operating state of the internalcombustion engine—preferably as a function of an exhaust gastemperature, an oxygen concentration and/or a mass flow of the exhaustgas flowing into the exhaust gas particle filter. Relatively exactinstantaneous values thus result across the entire regeneration process.

It is particularly preferred in this instance for the instantaneousvalue to be ascertained step-by-step by said instantaneous value beingrecalculated in regular intervals as a function of its current value andthe at least one state variable. Said instantaneous value is thereforeregularly updated according to a recursive calculation scheme during theregeneration process. At the beginning of said regeneration process, theinitial value mentioned above, which characterizes the mass of the sootsituated in the exhaust gas particle filter before the beginning of theregeneration process, can be used as the starting value for thesecalculations. The initial value can be ascertained in a suitable mannerby means of calculations during the operation of the internal combustionengine before the beginning of the regeneration process, in particularusing state variables of the internal combustion engine.

If the internal combustion engine is in the overrun mode, wherein nofuel is injected into the combustion chambers of the internal combustionengine, the gas flowing into the exhaust gas particle filtersubstantially corresponds to the ambient air and therefore has acomparatively high oxygen content of approximately 21 percent. Becausethe exothermal reaction relates to an oxidation, an especially largerisk exists in the overrun mode for too high of a reaction rate. It istherefore preferred for the method to be executed while the internalcombustion engine is being operated in said overrun mode. Moreover, theactuating elements of the internal combustion engine can be largelyfreely adjusted during the overrun mode because combustion processes inthe combustion chambers of the internal combustion engine in this casedo not have to be controlled in an open or closed loop. The method cantherefore be easily applied in the overrun mode.

As a further solution to the inventive aim mentioned above, theinvention is characterized by a control unit with the characteristics ofclaim 10. With the aid of a control unit of this type, the duration ofthe regeneration process can be reduced and said process can be reliablycontrolled. In this way, a high degree of regeneration efficiencyresults.

Particularly if the control unit is equipped for executing the inventivemethod, all of the advantages of said method can be realized. Thecontrol unit preferably has a computer, which is programmed forexecuting the inventive method and/or has a programmed storage forexecuting the inventive method.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional characteristics and advantages of the invention becomeapparent in the following description, wherein exemplary embodiments ofthe invention are explained in detail with the aid of the drawings. Thefollowing are thereby shown:

FIG. 1 is a schematic depiction of an internal combustion engine havinga control unit according to a preferred embodiment of the presentinvention;

FIG. 2 is a diagram that depicts a correlation between a soot mass, agas mass flow and a maximum temperature occurring in an exhaust gasparticle filter of the internal combustion engine shown in FIG. 1;

FIG. 3 is a flow diagram of a method for controlling a regenerationprocess of the exhaust gas particle filter;

FIG. 4 is a flow diagram of a sequence of the method immediately priorto the beginning of the regeneration process; and

FIG. 5 is a signal flow diagram of calculations for ascertaining aninstantaneous value of the soot mass.

DETAILED DESCRIPTION

An internal combustion engine 11 schematically depicted in FIG. 1 isconfigured in the embodiment shown as a diesel internal combustionengine. Said internal combustion engine 11 has an engine block 13 with aplurality of combustion chambers 15. Said internal combustion engine 11furthermore has an air and exhaust system 17. The air and exhaust system17 has an intake manifold 19 for drawing in the ambient air (arrow 21),wherein an air mass flow sensor 23 is disposed, which is configured inthe embodiment shown as a hot film mass flow sensor. A compressor 25 ofan exhaust gas turbocharger 27 of the air and exhaust gas system 17 isdisposed in the intake manifold 19 behind the air mass flow sensor 23 inthe direction of flow depicted by arrow 21. A throttle device 29 formanipulating, particularly for limiting, a mass flow m_(e) of the air 21flowing through the intake manifold 19 during the operation of theinternal combustion engine 11 is situated behind the compressor 25 inthe direction of flow of the intake air. A side of said throttle device29 facing away from the compressor 25 of the exhaust gas turbocharger 27is connected to an air inlet of the engine block 13 via a channel 31. Anexhaust gas outlet of the engine block 13 is connected to a turbine 33of the exhaust gas turbocharger 27 as well as to the channel 31 via anexhaust gas guide channel 35. An exhaust gas recirculation valveassembly 37 for manipulating a mass flow m_(AGR) of a gas flowingthrough the exhaust gas recirculation channel 35 during the operation ofthe internal combustion engine 11 is disposed in said exhaust gasrecirculation channel 35.

An oxidation catalytic converter 39 of the air and exhaust gas system17, which is followed by an exhaust gas particle filter 41 in thedirection of flow, is disposed behind the turbine 33 in said directionof flow (depicted in FIG. 1 by corresponding arrows). Additionalassemblies, as, for example, a muffler (not shown), of the air andexhaust gas system can be disposed behind said exhaust gas particlefilter 41 in the direction of flow.

A first temperature sensor 43 for acquiring a temperature of the gasflowing into the oxidation catalytic converter 39 is disposed betweenthe turbine 33 and the oxidation catalytic converter 39. A secondtemperature sensor 45 for acquiring a gas temperature of the gas 47flowing into the exhaust gas particle filter 41 is situated between saidoxidation catalytic converter 39 and said exhaust gas particle filter41. In addition, a lambda probe 49 for acquiring an oxygen concentration8 of the gas 47 flowing into said exhaust gas particle filter 41 isdisposed between said oxidation catalytic converter 39 and said exhaustgas particle filter 41. The lambda probe 49 in the exemplary embodimentshown relates to a broadband lambda probe. Deviating from the exemplaryembodiment shown, the oxidation catalytic converter 39 can also beomitted or be disposed at another location of the air and exhaust gassystem 17. It is, however, preferred that the second temperature sensor45 and the lambda probe 49 be disposed upstream of the exhaust gasparticle filter 41 in the direction of flow (arrow 47). The firsttemperature sensor 43, the second temperature sensor 45 and the lambdaprobe 49 are connected to a control unit 51 of the internal combustionengine 11. The control unit 51 is furthermore connected to an actuatingelement of the throttle device 29 as well as to an actuating element ofthe exhaust gas recirculation valve assembly 37. The two actuatingelements are configured as electromagnetic adjusting drives. Inaddition, said control unit 51 can activate the exhaust gas turbocharger27 for manipulating a boost pressure of the gas situated in the channel31. Provision can particularly be made for a closed-loop control of theboost pressure.

During the operation of the internal combustion engine 11, thecompressor 25 compresses the air 21 drawn in via the intake manifold 19.The air travels into the air inlet of the engine block 13 via thechannel 31 and from there to the individual combustion chambers 15within said engine block 13. If the internal combustion engine 11 is notin the overrun mode, fuel is then injected into the combustion chambers15 and is burned in said combustion chambers 15. The exhaust gasresulting from this combustion leaves the combustion chambers 15 andtravels to the turbine 33 of the exhaust gas turbocharger 27 via theexhaust gas outlet of the engine block 25 and hereby drives thecompressor 25 of said exhaust gas turbocharger 27. The gas flowing outof the turbine 33 is subsequently channeled through the oxidationcatalytic converter 39 and after that through the exhaust gas particlefilter 41 so that it finally leaves the exhaust gas particle filter 41as exhaust gas 53 and as the case may be is released to the atmosphereafter passing through additional components of the air and exhaust gassystem 17.

The control unit 51 adjusts a degree of opening of the throttle device29 by means of a first actuating signal s₁ and a degree of opening ofthe exhaust gas recirculation assembly 37 by means of a second actuatingsignal s₂. By predetermining certain values of the two actuating signalss₁ and s₂, the control unit 51 defines an exhaust gas recirculationrate, i.e. the mass flow m_(AGR) of that gas, which flows out of theexhaust gas outlet of the engine block 13 and is directed back to thechannel 31 via the exhaust gas recirculation channel 35. If the exhaustgas recirculation valve assembly 37 is not completely closed, an exhaustgas recirculation rate results that is different from zero so that amass flow m_(k) through the channel 31 is larger than a mass flow m_(e)of the air 21 flowing into the intake manifold 19 and a mass flow m_(a)of the gas 47 flowing into the exhaust gas particle filter 41.

During the operation of the internal combustion engine 11, the controlunit 51 controls the internal combustion engine 11 in a closed or openloop as a function of different operating variables of said internalcombustion engine 11. For this purpose, the air mass flow sensor 23generates an air mass flow signal m, which characterizes the mass flowm_(i) of the air flowing into the intake manifold 19. The firsttemperature sensor 43 acquires a temperature signal, which characterizesa temperature T_(o) of the gas flowing into the oxidation catalyticconverter 39. The second temperature sensor 45 correspondingly generatesan additional temperature signal, which characterizes the temperatureT_(p) of the gas flowing into the exhaust gas particle filter 41.Finally the lambda probe 49 generates a sensor signal, whichcharacterizes an oxygen concentration 8 of the gas flowing into theexhaust gas particle filter 41. The control unit 51 acquires thesesensor signals and ascertains actuating signals from them, like, forexample, the two actuating signals s₁ and s₂ shown in FIG. 1, foractivating actuators of said internal combustion engine 11 while usingsuitable open-loop and/or closed loop control methods.

Soot particles form during the combustion processes within thecombustion chambers 15 of the engine block 13, which are discharged outof the exhaust gas outlet of said engine block 13. If said sootparticles do not then travel into the exhaust gas recirculation channel35, they are directed through the oxidation catalytic converter 39 tothe exhaust gas particle filter 41. The exhaust gas particle filter 41retains the soot particles so that the gas discharging from said exhaustgas particle filter 41 is at least largely free of soot particles. Withtime the particles are deposited in the exhaust gas particle filter 41in the form of soot.

In order to in turn remove these soot deposits, the control unit 51carries out from time to time a regeneration process of the exhaust gasparticle filter 41, in which the soot deposits situated in the exhaustgas particle filter 41 are burned off. In so doing, the control unit 51adjusts to an operating state of the internal combustion engine 11,wherein a relatively high temperature T_(p) of the gas 47 flowing intothe exhaust gas particle filter 41 arises. In the embodiment shown, atemperature T_(p) of approximately 600EC to 650EC is adjusted. The hightemperature T_(p) of the gas 47 flowing into the exhaust gas particlefilter 41 can, for example, be achieved by suitable after injections offuel, which lead to additional combustions within the combustionchambers 15 or within the oxidation catalytic converter 39. At the sametime, an inward flow of fresh air, which lowers the temperature T_(p) ofthe incoming gas 47, can be reduced by at least partially closing thethrottle device 29.

Filter means of the exhaust gas particle filter 41 are heated up by thehigh temperature T_(p) of the inflowing gas 47 and an activation energyrequired for starting an exothermal reaction, wherein the soot depositsare burned off in the exhaust gas particle filter, is thereby provided.As soon as an exothermal reaction has been started, the control unit 51controls the regeneration process, such that the reaction rate of thisexothermal reaction remains so low that a maximally admissibletemperature within the exhaust gas particle filter is not exceeded. Ifnecessary the control unit 51 implements safeguards for protecting theexhaust gas particle filter 41 from overheating.

In the diagram shown in FIG. 2, a maximum temperature T_(max) within theexhaust gas particle filter 41 is depicted as a function of the massflow m_(a) of the gas 47 flowing into said exhaust gas particle filter41 and a total mass x of the soot deposits situated in said exhaust gasparticle filter 41. The mass flow m_(a) of the incoming gases is givenin kilograms per hour and the mass x of the soot deposits in grams. Themaximum temperature T. is given in EC and is depicted in the form ofnumerical values in the first quadrant of this diagram. The diagram wascreated for a temperature T_(p) of the incoming gas 47 of T_(p)=680ECand an oxygen content of the incoming gas 47 of 21%. A critical filtertemperature of said exhaust gas particle filter 41 amounts toapproximately 900EC in the embodiment shown. It can be seen from thediagram that maximum temperatures T., which are significantly lower thanthe critical filter temperature of 900EC, occur in a region of saiddiagram beneath a curve 55. It can furthermore be seen from the diagramthat the critical filter temperature is not achieved at a certaintemperature T_(p) of the incoming gas 47 if a certain minimum value ofthe mass x is undershot. In such a case, safeguards do not have to beimplemented during the regeneration process to protect the exhaust gasparticle filter from overheating. Provision is accordingly made in theembodiment shown for an instantaneous value, which characterizes theinstantaneous mass x of the soot situated in the exhaust gas particlefilter 41, to be ascertained during the regeneration process and for anuncritical operating state, wherein the safeguards do not have to beimplemented, to be recognized if the instantaneous value is smaller thana predetermined minimum value.

A method 61 for controlling the regeneration process of the exhaust gasparticle filter 41 is explained below in detail with the aid of FIG. 3.After the method has been started in step 63, a check is made in abranch 65 to determine whether a regeneration process is taking place,which can potentially lead to an overheating of the exhaust gas particlefilter 41. If that is not the case (N), the check is then repeated insaid branch 65 until it is recognized that such a potential criticalregeneration process is taking place (Y). In the simplest case, eachregeneration process is classified as potentially critical for thetemperature in the exhaust gas particle filter so that a check mustmerely be made to determine whether a regeneration process is currentlytaking place or not.

A check can additionally be made in branch 65 to determine whether theinternal combustion engine 11 is operating in an overrun mode. If thisis not the case (N), the branch 65 is repeated. With the exception ofbranch 65, the method 61 is therefore only then executed if saidinternal combustion engine 11 is operating in the overrun mode. Inderogation from the embodiment shown, said branch 65 can also beomitted.

A check is subsequently made in an additional branch 67 to determinewhether an uncritical operating state of the exhaust gas particle filter41 is present. In order to check whether an uncritical operating stateis present, an instantaneous value x(t), which characterizes theinstantaneous mass x of the soot in the exhaust gas particle filter 41,is compared with a predetermined minimum value x_(min). In addition thesensor signal T_(p), which characterizes the temperature of the gas 47flowing into the exhaust gas particle filter 41, is checked. If theinstantaneous value x_(t) is lower than the predetermined minimum valuex_(min), and the temperature T_(p) is lower than the predetermined firstminimum temperature, then (Y) the uncritical operating state isrecognized. In derogation from the embodiment shown, the check of thetemperature T_(p) of the incoming gas can be omitted and theinstantaneous value x(t) can merely be checked in branch 67.

In the event that the uncritical operating state is present, the methodbranches off to step 69, which opens the throttle device 29 in theoverrun mode. The method branches off to step 71 only in the event ofthe critical operating state being present, wherein the safeguards forprotecting the exhaust gas particle filter 41 from overheating areimplemented. The safeguards 71 comprise two steps 71 a and 71 b. In step71 a the degree of opening of the throttle device 29 is decreased; andin step 71 b following step 71 a, the degree of opening of the exhaustgas recirculation valve assembly 37 is increased. In total the mass flowm_(a) of the gas 47 flowing into the exhaust gas particle filter 41 isreduced by the two steps 71 a and 71 b of the safeguards 71. Inderogation from the embodiment shown, steps 71 a and 71 b can also beexecuted in the reverse order, simultaneously or temporally overlapping.

A check is made in branch 73 following step 69 to determine whether thetemperature of the incoming gas 47 is lower than a predetermined secondminimum temperature T_(min2). If this is the case (Y), the throttledevice 29 is then partially or completely closed in step 75 so that acooling of the exhaust gas particle filter 41, which can cause theexothermal reaction to come to a standstill, is avoided. Otherwise (N)the method returns to step 69.

Branch 67 generally ensures that the safeguards 71 are suppressed andthat steps 69, 73 are executed instead of said safeguards 71 if theexhaust gas particle filter 41 is in an uncritical operating state.

Provision can be made for a check to be performed in advance immediatelyprior to the beginning of the regeneration process to determine whetheran overheating of the exhaust gas particle filter 41 can be ruled outwith certainty. For this purpose, the sequence shown in FIG. 4 can, forexample, be used. An initial value x (0) of the mass of the sootsituated in said exhaust gas particle filter 41 immediately before thebeginning of the regeneration process is first ascertained in step 79using values, which refer to the operating state of the internalcombustion engine 11, respectively said exhaust gas particle filter 41,immediately before the beginning of the regeneration process.Subsequently in step 81 in particular as a function of the initial valuex(0) a temperature T_(e) is estimated, which corresponds to ananticipated maximum temperature within said particle filter 41.Deviating from this, another parameter can be ascertained instead of theestimated temperature T_(e), which indicates the maximum thermal load ofthe exhaust gas particle filter 41. In step 83 following step 81, acheck is made particularly as a function of the estimated T_(e) as towhether the temperature in the exhaust gas particle filter 41 isanticipated to be too high during the regeneration process. The resultof this check is stored for the use thereof in branch 65.

In one embodiment, wherein the sequence in FIG. 4 is provided, theresult stored in step 83 is additionally checked in the branch 65. Inthe event that a result has been stored, which indicates that thetemperature in the exhaust gas particle filter 41 is not anticipated tobe too high during the regeneration process, branch 65 is repeated. Thesequence shown in FIG. 4 therefore makes a pre-decision as to whetherthe safeguards are potentially needed. If it turns out during theregeneration process that the safeguards are not or are no longerrequired, said safeguards are then suppressed independently of theresult of the pre-decision. In so doing it can also occur that thesafeguards 71 are, for example, implemented at the beginning of theregeneration process and if the instantaneous value x(t) has dropped asufficient amount that said safeguards 71 are lifted towards the end ofsaid regeneration process. This is the case because the decision inbranch 67 ensures that steps 69, 73 and 75 are executed after a certainlength of time of the regeneration process.

FIG. 5 shows a signal flow diagram, wherein it is schematically depictedhow the instantaneous value x(t) of the soot mass x is ascertained inbranch 67. A calculation block 85 calculates the instantaneous valuex(t) in regular, preferably in periodically repeated, time intervals Δtas a function of the temperature T_(p) of the gas flowing into theexhaust gas particle filter 41, the oxygen concentration 8 of theincoming gas 47, the mass flow m_(a) of the incoming gas 47 as well as astored value x (t-At) of the instantaneous value x(t). The storedinstantaneous value x (t-At) is provided by a storage element 87. Aninput of said storage element 87 is connected to an output of thecalculation block 85 for this purpose. Provision can be made for theinitial value x(0) to be deposited into the storage element 87immediately before the beginning of the regeneration process.

In total the present invention provides a method 61, with which on theone hand an unnecessary restriction of the reaction rate duringregeneration of the exhaust gas particle filter 41 is avoided and in sodoing a fast and more reliable regeneration is made possible, and on theother hand a cooling of said exhaust gas particle filter 41 is avoidedduring said regeneration process as a result of a relatively lowtemperature T_(p) of the gas 47 flowing into the exhaust gas particlefilter 41. In this way, a considerable improvement of the regenerationefficiency is achieved and in so doing the fuel consumption of theinternal combustion engine 11 is reduced.

1. Method for controlling a regeneration process of an exhaust gasparticle filter of an internal combustion engine, wherein said methodcomprises safeguards for protecting the exhaust gas particle filter fromoverheating and when implementing said safeguards a gas flow of gasflowing through the exhaust gas particle filter is reduced for thepurpose of restricting a reaction rate of an exothermal reaction takingplace in the exhaust gas particle filter during the regenerationprocess, wherein an instantaneous value, which characterizes aninstantaneous mass of the soot situated in the exhaust gas particlefilter, is ascertained during the regeneration process, a check is madeas a function of said instantaneous value to determine whether theexhaust gas particle filter is in an uncritical operating state and saidsafeguards are suppressed in the event that said uncritical operatingstate is present.
 2. The method according to claim 1, wherein theuncritical operating state is recognized in the event that theinstantaneous value is smaller than a predetermined minimum value. 3.The method according to claim 1, wherein the uncritical operating stateis recognized in the event that a gas temperature of the gas flowinginto the exhaust gas particle filter is lower than a predetermined firstminimum temperature.
 4. The method according to claim 2, wherein aninitial value is ascertained, which characterizes the mass of the sootsituated in the exhaust gas particle filter before the beginning of theregeneration process, and a check is made as a function of said initialvalue to determine whether the reaction rate is anticipated to be toohigh, and the safeguards are only then implemented in the event that thecheck resulted in the reaction rate being anticipated to be too high. 5.The method according to claim 1, wherein the gas flow is reduced toavoid a cooling of the exhaust gas particle filter in the event that thegas temperature is lower than a predetermined second minimumtemperature.
 6. The method according to claim 1, wherein the gas flow ismanipulated by positioning actuating elements of an air and exhaust gassystem of the internal combustion engine, preferably by adjusting adegree of opening of a throttle device and/or of an exhaust gasrecirculation valve assembly.
 7. The method according to claim 1,wherein the instantaneous value is ascertained as a function of at leastone state variable, which characterizes an operating state of theinternal combustion engine, preferably as a function of an exhaust gastemperature, an oxygen concentration and/or a mass flow of the gasflowing into the exhaust gas particle filter.
 8. The method according toclaim 7, wherein the instantaneous value is ascertained in steps by saidinstantaneous value being recalculated in regular intervals as afunction of its current value and the at least one state variable. 9.The method according to claim 1, wherein the method is executed whilethe internal combustion engine is operating in the overrun mode. 10.Control unit for the open-loop and/or closed-loop control of an internalcombustion engine, which has an exhaust gas system with an exhaust gasparticle filter, said control unit being equipped for controlling aregeneration process of the exhaust gas particle filter such that it canimplement safeguards for protecting said exhaust gas particle filterfrom overheating, a gas flow of gas flowing through said exhaust gasparticle filter being reduced when implementing said safeguards for thepurpose of restricting a reaction rate of an exothermal reaction takingplace in said exhaust gas particle filter during the regenerationprocess, wherein said control unit is equipped such that during theregeneration process an instantaneous value, which characterizes aninstantaneous mass of the soot situated in said exhaust gas particlefilter, is ascertained, a check is made as a function of saidinstantaneous value to determine whether said exhaust gas particlefilter is in an uncritical operating state and said safeguards aresuppressed in the event that the uncritical operating state is present.11. The control unit according to claim 10, wherein it is equipped,preferably is programmed, for executing a method according to claim 1.